RU2042880C1 - Method of step combustion of fuel-air mixture - Google Patents

Abstract

FIELD: heat power engineering. SUBSTANCE: furnace chamber is provided with zone 1 of active combustion, reduction zone 2, and afterburning zone 3. Main portion of fuel 4 and air 5 is fed to zone 1 of active combustion through main burners. The remainder portion of fuel and auxiliary fuel 6 together with transporting fluid are fed to the furnace above the main burning collar through a set of slots made in bounding surfaces, i.e. to the reduction zone 2. Portion of air 8, which is required for afterburning products of incomplete combustion, is directed to afterburning zone 3. Auxiliary fuel 6 and transporting fluid 7 are fed to reduction zone 2 and air 8 is fed to zone 3 of afterburning as vortex jets. EFFECT: enhanced efficiency. 2 dwg

Description

 The invention relates to a power system and can be used in pulverized coal boilers.

 Staged combustion of the air-fuel mixture in coal-fired boilers is an effective way to reduce nitrogen oxide emissions.

 Staged combustion can be implemented in various ways, for example, by discharging part of the air into the furnace in addition to the burners, redistributing the fuel or air between the tiers of the burners in the furnaces with a multi-level arrangement of the burners, and in pulverized coal boilers equipped with vacuum systems with an industrial hopper, increasing the supply of fuel to the lower burners without changing the distribution of air between the burners of all tiers, which provide a different frequency of rotation of dust collectors associated with the upper and lower burners.

 Known methods of staged combustion [1-3] similar to the proposed.

 One of the most effective technological methods of suppressing nitrogen oxide emissions in the combustion process is a three-stage fuel combustion, which provides for the organization in the upper part of the furnace of the reduction zone, where nitrogen oxides are reduced to molecular nitrogen. As a reducing medium, products of incomplete combustion of a portion of the main or auxiliary fuel are used, carbon monoxide, hydrogen, hydrogen sulfide, as well as intermediate unstable combustion products, scraps of reaction chains, radicals, and active centers.

 The small mass of fuel necessary to obtain a reducing medium does not allow to organize its uniform distribution over the cross section of the combustion chamber. Therefore, the introduction of auxiliary fuel into the recovery zone is carried out in a mixture with a significant mass of the transporting medium: air or flue gases. The mixture of the transporting medium and auxiliary fuel is introduced into the furnace through a series of splines transverse (or at some angle) to the upward high-temperature flow of flue gases. Simultaneously with the aerodynamic processes of the development of the jet of the specified mixture, its partial burnout and the formation of a reducing medium occur. The length of the reduction zone should provide a residence time of at least 600 ms of combustion products from the main burners in this zone. During this time, mainly the processes of reduction of nitrogen oxides are completed.

 Given the limited height of the combustion chamber, it can be stated that the efficiency of three-stage combustion will largely depend on the degree of uniformity of the distribution of the reducing medium in the cross section of the combustion chamber, which, taking into account the large size of the combustion chamber (in plan), is a difficult engineering task.

 Currently, the introduction of the reducing medium into the furnace is carried out by a system of direct-flow jets.

 Closest to the proposed method of burning the air-fuel mixture is the method [4] This method of staged burning of the air-fuel mixture in coal-fired boilers equipped with furnaces with more than two tiers of burners provides for the supply of fuel by redistributing it between the tiers of the burners so that part of the fuel is fed to the main burners lower tier, the remaining amount of fuel and auxiliary fuel together with the transporting medium is introduced into the middle tier above the main burners transversely to the flue stream gases, and in the upper tier of burners supplied with air, necessary for afterburning products of incomplete fuel combustion.

 The disadvantage of this method is that when introducing a reducing medium into the furnace, direct-flow jets to sufficiently fill the volume of the furnace with a relatively small opening angle of straight-through jets requires a large number of slots for introducing a reducing medium. This complicates the design of the boiler, the piping system of the boiler with air and gas pipelines, and, accordingly, the conditions of operation and maintenance of the boiler. In addition, slots of various sizes should be made, which will provide different range of individual jets of the recovery medium. Similar problems exist when introducing air for afterburning.

 In order to eliminate these drawbacks and increase the efficiency of suppressing nitrogen oxides in the proposed method of staged combustion of the air-fuel mixture in pulverized coal boilers equipped with furnaces with more than two tiers of burners, by redistributing fuel between the tiers of the burners so that part of the fuel is fed to the burners of the main lower tier, the rest the amount of fuel and auxiliary fuel together with the transporting medium is introduced into the middle tier above the main burners transversely to the flue gas flow, and to the top rd tier of burners supplied with air, necessary for afterburning products of incomplete fuel combustion, the fuel mixture with air and conveying medium supplied to the middle and upper tiers of the burners are introduced into the furnace in a swirling jets.

 In FIG. 1 and 2 presents a diagram of the implementation of the proposed method for staged combustion of the air-fuel mixture in pulverized coal boilers.

 In FIG. Figure 1 shows a three-stage combustion scheme with the introduction of a mixture of auxiliary fuel and a transporting medium into the recovery zone, with air supplied to the afterburning zone in the form of swirling flows. Thus, here both reducing and oxidizing media enter the furnace as a system of transverse vortex jets.

 Three zones are distinguished in height in the combustion chamber: active combustion zone 1, reduction zone 2, and afterburning zone 3.

 The main part of the estimated fuel consumption 4 and air 5 is fed into the active combustion zone 1 through the main burners (first, lower tier burners). The rest of the fuel or auxiliary fuel 6 together with the transporting medium 7 is fed into the furnace above the main burner belt through a series of splines on the enclosing surfaces, i.e. to recovery zone 2.

 Part of the air 8 necessary for the afterburning of products of incomplete combustion is directed to the afterburning zone 3.

 The mixture of auxiliary fuel 6 and the transporting medium 7 is introduced into the reduction zone 2, as well as air 8 into the afterburning zone 3 in the form of vortex jets.

 In FIG. 2 shows a cross section of a furnace, a variant of organizing three-stage combustion with alternating vortex 9 and direct-flow jets of reducing and oxidizing media is presented.

 The implementation of the proposed solution is ensured by making round-shaped embrasures in the enclosing surfaces of the furnace for introducing reducing and oxidizing media with the placement of blade swirlers in them.

 Due to the larger opening angle than direct-flow jets, it is possible to cover a significantly larger part of the furnace section by the influence of each slot with a twisting device. In the same section of the furnace, in height, the diameter of the jet trace after being deepened into a blowing flue gas stream in the case of twisting turns out to be 2-2.5 times larger than in the case of direct flow.

 A comparative analysis of the results of calculations performed for the TPP-804 boiler of a 800 MW unit shows that when the air-fuel mixture is fed into the recovery zone, the transition from direct-flow jets to swirling jets increases the degree of filling of the furnace section with a reducing medium from 0.38 to 0.65.

Claims (1)

 METHOD FOR STEADY BURNING OF FUEL-AIR MIXTURE in pulverized-coal boilers with furnaces having more than two tiers of burners by redistributing fuel between the tiers of the burners so that part of the fuel is fed into the burners of the lower tier, the remaining amount of fuel and auxiliary fuel are introduced into the transporting medium into the transporting medium above the main burners transverse to the flue gas stream, and air is supplied to the upper tier of the burners necessary for afterburning products of incomplete fuel combustion, characterized in that the fuel mixture with the transporting medium and air supplied respectively to the middle and upper tiers of the burners, are introduced into the furnace in the form of swirling jets.

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